1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a direct current (DC) to DC converter, and more particularly, to a flyback converter in which a quasi-resonant topology is applied.
2. Description of the Related Art
A related art flyback converter such as a flyback converter with a quasi-resonant topology will be described with reference to FIG. 1. As shown in FIG. 1, the related art flyback converter comprises an input voltage Vin, a transformer T0 which has a primary winding 100 and a secondary winding 200, and a circuit device such as a metal oxide semiconductor field effect transistor (MOSFET) switch which is repeatedly turned on/off according to a control signal.
The input voltage Vin is converted by the transformer T0 according to a turn-on/turn-off state of the MOSFET and is output to DC voltage. However, a switching loss occurs during a turn-on/turn-off state of the MOSFET because the related art flyback converter utilizes energy-conversion when devices such as the MOSFET are used for high-speed switching.
To decrease the switching loss, the quasi-resonant topology is applied to the flyback converter. The flyback converter according to the quasi-resonant topology senses a voltage output from the primary winding 100 when the MOSFET is turned-off based on a minimum voltage of the MOSFET and then turns-on the MOSFET when an output voltage Vout becomes the minimum voltage. Accordingly, the switching loss of the flyback converter of the quasi-resonant topology can be decreased when compared with the related art flyback converter when the MOSFET is turned-on.
Also, as shown in FIG. 1, a capacitor Co is connected in parallel with the MOSFET, thereby decreasing a spike of the MOSFET drain-source voltage Vds according to a turn-off state of the MOSFET.
However, in the flyback converter of the quasi-resonant topology, the capacitor Co is discharged through the MOSFET when the MOSFET is turned on. Accordingly, a large lead edge current occurs, resulting in switching loss of the MOSFET when the MOSFET is turned-on.